<!DOCTYPE html>
<html lang="zh" dir="ltr" class="client-nojs">
<head>
<title>赋值运算符</title>
<meta charset="UTF-8">
<meta name="generator" content="MediaWiki 1.21.2">
<link rel="shortcut icon" href="../../../common/favicon.ico">
<link rel="stylesheet" href="../../../common/ext.css">
<meta name="ResourceLoaderDynamicStyles" content="">
<link rel="stylesheet" href="../../../common/site_modules.css">
<style>a:lang(ar),a:lang(ckb),a:lang(fa),a:lang(kk-arab),a:lang(mzn),a:lang(ps),a:lang(ur){text-decoration:none}#toc{display:none}.editsection{display:none}
/* cache key: mwiki1-mwiki_zh_:resourceloader:filter:minify-css:7:15cea3ec788a65b5187d4018eed543bf */</style>

<script src="../../../common/startup_scripts.js"></script>
<script>if(window.mw){
mw.config.set({"wgCanonicalNamespace":"","wgCanonicalSpecialPageName":false,"wgNamespaceNumber":0,"wgPageName":"cpp/language/operator_assignment","wgTitle":"cpp/language/operator assignment","wgCurRevisionId":64608,"wgArticleId":2736,"wgIsArticle":true,"wgAction":"view","wgUserName":null,"wgUserGroups":["*"],"wgCategories":["Todo no example"],"wgBreakFrames":false,"wgPageContentLanguage":"zh","wgSeparatorTransformTable":["",""],"wgDigitTransformTable":["",""],"wgDefaultDateFormat":"zh","wgMonthNames":["","1月","2月","3月","4月","5月","6月","7月","8月","9月","10月","11月","12月"],"wgMonthNamesShort":["","1月","2月","3月","4月","5月","6月","7月","8月","9月","10月","11月","12月"],"wgRelevantPageName":"cpp/language/operator_assignment","wgUserVariant":"zh","wgRestrictionEdit":[],"wgRestrictionMove":[]});
}</script><script>if(window.mw){
mw.loader.implement("user.options",function(){mw.user.options.set({"ccmeonemails":0,"cols":80,"date":"default","diffonly":0,"disablemail":0,"disablesuggest":0,"editfont":"default","editondblclick":0,"editsection":0,"editsectiononrightclick":0,"enotifminoredits":0,"enotifrevealaddr":0,"enotifusertalkpages":1,"enotifwatchlistpages":0,"extendwatchlist":0,"externaldiff":0,"externaleditor":0,"fancysig":0,"forceeditsummary":0,"gender":"unknown","hideminor":0,"hidepatrolled":0,"imagesize":2,"justify":0,"math":1,"minordefault":0,"newpageshidepatrolled":0,"nocache":0,"noconvertlink":0,"norollbackdiff":0,"numberheadings":0,"previewonfirst":0,"previewontop":1,"quickbar":5,"rcdays":7,"rclimit":50,"rememberpassword":0,"rows":25,"searchlimit":20,"showhiddencats":0,"showjumplinks":1,"shownumberswatching":1,"showtoc":0,"showtoolbar":1,"skin":"cppreference2","stubthreshold":0,"thumbsize":2,"underline":2,"uselivepreview":0,"usenewrc":0,"watchcreations":0,"watchdefault":0,"watchdeletion":0,
"watchlistdays":3,"watchlisthideanons":0,"watchlisthidebots":0,"watchlisthideliu":0,"watchlisthideminor":0,"watchlisthideown":0,"watchlisthidepatrolled":0,"watchmoves":0,"wllimit":250,"variant":"zh","language":"zh","searchNs0":true,"searchNs1":false,"searchNs2":false,"searchNs3":false,"searchNs4":false,"searchNs5":false,"searchNs6":false,"searchNs7":false,"searchNs8":false,"searchNs9":false,"searchNs10":false,"searchNs11":false,"searchNs12":false,"searchNs13":false,"searchNs14":false,"searchNs15":false,"gadget-MathJax":1,"gadget-ColiruCompiler":1});;},{},{});mw.loader.implement("user.tokens",function(){mw.user.tokens.set({"editToken":"+\\","patrolToken":false,"watchToken":false});;},{},{});
/* cache key: mwiki1-mwiki_zh_:resourceloader:filter:minify-js:7:258d7cd6aa9aa67dee25e01fb6a9e505 */
}</script>
<script>if(window.mw){
mw.loader.load(["mediawiki.page.startup","mediawiki.legacy.wikibits","mediawiki.legacy.ajax"]);
}</script>
<style type="text/css">/*<![CDATA[*/
.source-cpp {line-height: normal;}
.source-cpp li, .source-cpp pre {
	line-height: normal; border: 0px none white;
}
/**
 * GeSHi Dynamically Generated Stylesheet
 * --------------------------------------
 * Dynamically generated stylesheet for cpp
 * CSS class: source-cpp, CSS id: 
 * GeSHi (C) 2004 - 2007 Nigel McNie, 2007 - 2008 Benny Baumann
 * (http://qbnz.com/highlighter/ and http://geshi.org/)
 * --------------------------------------
 */
.cpp.source-cpp .de1, .cpp.source-cpp .de2 {font: normal normal 1em/1.2em monospace; margin:0; padding:0; background:none; vertical-align:top;}
.cpp.source-cpp  {font-family:monospace;}
.cpp.source-cpp .imp {font-weight: bold; color: red;}
.cpp.source-cpp li, .cpp.source-cpp .li1 {font-weight: normal; vertical-align:top;}
.cpp.source-cpp .ln {width:1px;text-align:right;margin:0;padding:0 2px;vertical-align:top;}
.cpp.source-cpp .li2 {font-weight: bold; vertical-align:top;}
.cpp.source-cpp .kw1 {color: #0000dd;}
.cpp.source-cpp .kw2 {color: #0000ff;}
.cpp.source-cpp .kw3 {color: #0000dd;}
.cpp.source-cpp .kw4 {color: #0000ff;}
.cpp.source-cpp .co1 {color: #909090;}
.cpp.source-cpp .co2 {color: #339900;}
.cpp.source-cpp .coMULTI {color: #ff0000; font-style: italic;}
.cpp.source-cpp .es0 {color: #008000; font-weight: bold;}
.cpp.source-cpp .es1 {color: #008000; font-weight: bold;}
.cpp.source-cpp .es2 {color: #008000; font-weight: bold;}
.cpp.source-cpp .es3 {color: #008000; font-weight: bold;}
.cpp.source-cpp .es4 {color: #008000; font-weight: bold;}
.cpp.source-cpp .es5 {color: #008000; font-weight: bold;}
.cpp.source-cpp .br0 {color: #008000;}
.cpp.source-cpp .sy0 {color: #008000;}
.cpp.source-cpp .sy1 {color: #000080;}
.cpp.source-cpp .sy2 {color: #000040;}
.cpp.source-cpp .sy3 {color: #000040;}
.cpp.source-cpp .sy4 {color: #008080;}
.cpp.source-cpp .st0 {color: #008000;}
.cpp.source-cpp .nu0 {color: #000080;}
.cpp.source-cpp .nu6 {color: #000080;}
.cpp.source-cpp .nu8 {color: #000080;}
.cpp.source-cpp .nu12 {color: #000080;}
.cpp.source-cpp .nu16 {color:#000080;}
.cpp.source-cpp .nu17 {color:#000080;}
.cpp.source-cpp .nu18 {color:#000080;}
.cpp.source-cpp .nu19 {color:#000080;}
.cpp.source-cpp .ln-xtra, .cpp.source-cpp li.ln-xtra, .cpp.source-cpp div.ln-xtra {background-color: #ffc;}
.cpp.source-cpp span.xtra { display:block; }

/*]]>*/
</style><style type="text/css">/*<![CDATA[*/
.source-text {line-height: normal;}
.source-text li, .source-text pre {
	line-height: normal; border: 0px none white;
}
/**
 * GeSHi Dynamically Generated Stylesheet
 * --------------------------------------
 * Dynamically generated stylesheet for text
 * CSS class: source-text, CSS id: 
 * GeSHi (C) 2004 - 2007 Nigel McNie, 2007 - 2008 Benny Baumann
 * (http://qbnz.com/highlighter/ and http://geshi.org/)
 * --------------------------------------
 */
.text.source-text .de1, .text.source-text .de2 {font: normal normal 1em/1.2em monospace; margin:0; padding:0; background:none; vertical-align:top;}
.text.source-text  {font-family:monospace;}
.text.source-text .imp {font-weight: bold; color: red;}
.text.source-text li, .text.source-text .li1 {font-weight: normal; vertical-align:top;}
.text.source-text .ln {width:1px;text-align:right;margin:0;padding:0 2px;vertical-align:top;}
.text.source-text .li2 {font-weight: bold; vertical-align:top;}
.text.source-text .ln-xtra, .text.source-text li.ln-xtra, .text.source-text div.ln-xtra {background-color: #ffc;}
.text.source-text span.xtra { display:block; }

/*]]>*/
</style><!--[if lt IE 7]><style type="text/css">body{behavior:url("/mwiki/skins/cppreference2/csshover.min.htc")}</style><![endif]--></head>
<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_language_operator_assignment skin-cppreference2 action-view cpp-navbar">
        <!-- header -->
        <!-- /header -->
        <!-- content -->
<div id="cpp-content-base">
            <div id="content">
                <a id="top"></a>
                <div id="mw-js-message" style="display:none;"></div>
                                <!-- firstHeading -->
<h1 id="firstHeading" class="firstHeading">赋值运算符</h1>
                <!-- /firstHeading -->
                <!-- bodyContent -->
                <div id="bodyContent">
                                        <!-- tagline -->
                    <div id="siteSub">来自cppreference.com</div>
                    <!-- /tagline -->
                                        <!-- subtitle -->
                    <div id="contentSub"><span class="subpages">&lt; <a href="../../cpp.html" title="cpp">cpp</a>‎ | <a href="../language.html" title="cpp/language">language</a></span></div>
                    <!-- /subtitle -->
                                                            <!-- bodycontent -->
                    <div id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr"><div class="t-navbar" style=""><div class="t-navbar-sep"> </div><div class="t-navbar-head"><a href="../../cpp.html" title="cpp"> C++</a><div class="t-navbar-menu"><div><div><table class="t-nv-begin" cellpadding="0" style="line-height:1.1em;">
<tr class="t-nv"><td colspan="5"> <a href="../language.html" title="cpp/language">语言</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../header.html" title="cpp/header">标准库头文件</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../freestanding.html" title="cpp/freestanding"> 自立与有宿主实现</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../named_req.html" title="cpp/named req">具名要求</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../utility.html#.E8.AF.AD.E8.A8.80.E6.94.AF.E6.8C.81" title="cpp/utility">语言支持库</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../concepts.html" title="cpp/concepts">概念库</a> <span class="t-mark-rev t-since-cxx20">(C++20)</span> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../error.html" title="cpp/error">诊断库</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../utility.html" title="cpp/utility">工具库</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../string.html" title="cpp/string">字符串库</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="https://zh.cppreference.com/w/cpp/container" title="cpp/container">容器库</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../iterator.html" title="cpp/iterator">迭代器库</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../ranges.html" title="cpp/ranges"> 范围库</a> <span class="t-mark-rev t-since-cxx20">(C++20)</span> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../algorithm.html" title="cpp/algorithm">算法库</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../numeric.html" title="cpp/numeric">数值库</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../io.html" title="cpp/io">输入/输出库</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../locale.html" title="cpp/locale">本地化库</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../regex.html" title="cpp/regex">正则表达式库</a> <span class="t-mark-rev t-since-cxx11">(C++11)</span> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../atomic.html" title="cpp/atomic">原子操作库</a> <span class="t-mark-rev t-since-cxx11">(C++11)</span> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../thread.html" title="cpp/thread">线程支持库</a> <span class="t-mark-rev t-since-cxx11">(C++11)</span> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../filesystem.html" title="cpp/filesystem">文件系统库</a> <span class="t-mark-rev t-since-cxx17">(C++17)</span> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../experimental.html" title="cpp/experimental">技术规范</a> </td></tr>
</table></div><div></div></div></div></div><div class="t-navbar-sep"> </div><div class="t-navbar-head"><a href="../language.html" title="cpp/language">C++ 语言</a></div><div class="t-navbar-sep"> </div><div class="t-navbar-head"><a href="expressions.html" title="cpp/language/expressions"> 表达式</a><div class="t-navbar-menu"><div><div style="display:inline-block">
<div><table class="t-nv-begin" cellpadding="0" style="">
<tr class="t-nv-h2"><td colspan="5"> 概述 </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="value_category.html" title="cpp/language/value category"> 值类别</a>（左值 lvalue、右值 rvalue、亡值 xvalue）</td></tr>
<tr class="t-nv"><td colspan="5"> <a href="eval_order.html" title="cpp/language/eval order"> 求值顺序</a>（序列点）</td></tr>
<tr class="t-nv"><td colspan="5"> <a href="constant_expression.html" title="cpp/language/constant expression"> 常量表达式</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="expressions.html#.E4.B8.8D.E6.B1.82.E5.80.BC.E8.A1.A8.E8.BE.BE.E5.BC.8F" title="cpp/language/expressions"> 不求值表达式</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="expressions.html#.E5.88.9D.E7.AD.89.E8.A1.A8.E8.BE.BE.E5.BC.8F" title="cpp/language/expressions"> 初等表达式</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="lambda.html" title="cpp/language/lambda">lambda 表达式</a><span class="t-mark-rev t-since-cxx11">(C++11)</span></td></tr>
<tr class="t-nv-h2"><td colspan="5"> 字面量 </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="integer_literal.html" title="cpp/language/integer literal">整数字面量</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="floating_literal.html" title="cpp/language/floating literal">浮点字面量</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="bool_literal.html" title="cpp/language/bool literal">布尔字面量</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="character_literal.html" title="cpp/language/character literal">字符字面量</a>，包含<a href="escape.html" title="cpp/language/escape">转义序列</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="string_literal.html" title="cpp/language/string literal">字符串字面量</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="nullptr.html" title="cpp/language/nullptr">空指针字面量</a><span class="t-mark-rev t-since-cxx11">(C++11)</span></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="user_literal.html" title="cpp/language/user literal">用户定义字面量</a><span class="t-mark-rev t-since-cxx11">(C++11)</span></td></tr>
<tr class="t-nv-h2"><td colspan="5"> 运算符 </td></tr>
<tr class="t-nv"><td colspan="5"> <strong class="selflink"> 赋值运算符</strong>:
<code>a=b</code>, <code>a+=b</code>, <code>a-=b</code>, <code>a*=b</code>, <code>a/=b</code>, <code>a%=b</code>, <code>a&amp;=b</code>, <code>a|=b</code>, <code>a^=b</code>, <code>a&lt;&lt;=b</code>, <code>a&gt;&gt;=b</code></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="operator_incdec.html" title="cpp/language/operator incdec"> 自增与自减</a>: <code>++a</code>, <code>--a</code>, <code>a++</code>, <code>a--</code></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="operator_arithmetic.html" title="cpp/language/operator arithmetic"> 算术运算符</a>:
<code>+a</code>, <code>-a</code>, <code>a+b</code>, <code>a-b</code>, <code>a*b</code>, <code>a/b</code>, <code>a%b</code>, <code>~a</code>, <code>a&amp;b</code>, <code>a|b</code>, <code>a^b</code>, <code>a&lt;&lt;b</code>, <code>a&gt;&gt;b</code> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="operator_logical.html" title="cpp/language/operator logical"> 逻辑运算符</a>: <code>a||b</code>, <code>a&amp;&amp;b</code>, <code>!a</code></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="operator_comparison.html" title="cpp/language/operator comparison"> 比较运算符</a>: <code>a==b</code>, <code>a!=b</code>, <code>a&lt;b</code>, <code>a&gt;b</code>, <code>a&lt;=b</code>, <code>a&gt;=b</code>, <code>a&lt;=&gt;b</code><span class="t-mark-rev t-since-cxx20">(C++20)</span></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="operator_member_access.html" title="cpp/language/operator member access"> 成员访问运算符</a>: <code>a[b]</code>, <code>*a</code>, <code>&amp;a</code>, <code>a-&gt;b</code>, <code>a.b</code>, <code>a-&gt;*b</code>, <code>a.*b</code></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="operator_other.html" title="cpp/language/operator other"> 其他运算符</a>: <code>a(...)</code>, <code>a,b</code>, <code>a?b:c</code> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="default_comparisons.html" title="cpp/language/default comparisons">默认比较</a><span class="t-mark-rev t-since-cxx20">(C++20)</span></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="operator_alternative.html" title="cpp/language/operator alternative">运算符的代用表示</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="operator_precedence.html" title="cpp/language/operator precedence">优先级和结合性</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="fold.html" title="cpp/language/fold">折叠表达式</a><span class="t-mark-rev t-since-cxx17">(C++17)</span></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="new.html" title="cpp/language/new">new 表达式</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="delete.html" title="cpp/language/delete">delete 表达式</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="throw.html" title="cpp/language/throw">throw 表达式</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="alignof.html" title="cpp/language/alignof">alignof</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="sizeof.html" title="cpp/language/sizeof">sizeof</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="sizeof....html" title="cpp/language/sizeof...">sizeof...</a><span class="t-mark-rev t-since-cxx11">(C++11)</span></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="typeid.html" title="cpp/language/typeid">typeid</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="noexcept.html" title="cpp/language/noexcept">noexcept</a><span class="t-mark-rev t-since-cxx11">(C++11)</span></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="operators.html" title="cpp/language/operators">运算符重载</a></td></tr>
<tr class="t-nv-h2"><td colspan="5"> 类型转换 </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="implicit_cast.html" title="cpp/language/implicit conversion">隐式转换</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="const_cast.html" title="cpp/language/const cast">const_cast</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="static_cast.html" title="cpp/language/static cast">static_cast</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="reinterpret_cast.html" title="cpp/language/reinterpret cast">reinterpret_cast</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="dynamic_cast.html" title="cpp/language/dynamic cast">dynamic_cast</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="explicit_cast.html" title="cpp/language/explicit cast">显式转换</a> <code>(T)a</code>, <code>T(a)</code></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="cast_operator.html" title="cpp/language/cast operator">用户定义转换</a></td></tr>
</table></div>
</div><div></div></div></div></div><div class="t-navbar-sep"> </div></div>
<p>赋值运算符修改对象的值。
</p>
<table class="wikitable" style="font-size:85%;">

<tr>
<th rowspan="2"> 运算符名
</th>
<th rowspan="2"> 语法
</th>
<th rowspan="2"> <a href="operators.html" title="cpp/language/operators">可重载</a>
</th>
<th colspan="2"> 原型示例（对于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">class</span> T</span></span>）
</th></tr>
<tr>
<th> 类内定义
</th>
<th> 类外定义
</th></tr>
<tr>
<td> 简单赋值
</td>
<td> <code>a = b</code>
</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">是
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp">T<span class="sy3">&amp;</span> T<span class="sy4">::</span><span class="me2">operator</span> <span class="sy1">=</span><span class="br0">(</span><span class="kw4">const</span> T2<span class="sy3">&amp;</span> b<span class="br0">)</span><span class="sy4">;</span></span></span>
</td>
<td style="background: #ececec; color: grey; vertical-align: middle; text-align: center;" class="table-na"> <small>N/A</small>
</td></tr>
<tr>
<td> 加法赋值
</td>
<td> <code>a += b</code>
</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">是
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp">T<span class="sy3">&amp;</span> T<span class="sy4">::</span><span class="me2">operator</span> <span class="sy2">+</span><span class="sy1">=</span><span class="br0">(</span><span class="kw4">const</span> T2<span class="sy3">&amp;</span> b<span class="br0">)</span><span class="sy4">;</span></span></span>
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp">T<span class="sy3">&amp;</span> operator <span class="sy2">+</span><span class="sy1">=</span><span class="br0">(</span>T<span class="sy3">&amp;</span> a, <span class="kw4">const</span> T2<span class="sy3">&amp;</span> b<span class="br0">)</span><span class="sy4">;</span></span></span>
</td></tr>
<tr>
<td> 减法赋值
</td>
<td> <code>a -= b</code>
</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">是
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp">T<span class="sy3">&amp;</span> T<span class="sy4">::</span><span class="me2">operator</span> <span class="sy2">-</span><span class="sy1">=</span><span class="br0">(</span><span class="kw4">const</span> T2<span class="sy3">&amp;</span> b<span class="br0">)</span><span class="sy4">;</span></span></span>
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp">T<span class="sy3">&amp;</span> operator <span class="sy2">-</span><span class="sy1">=</span><span class="br0">(</span>T<span class="sy3">&amp;</span> a, <span class="kw4">const</span> T2<span class="sy3">&amp;</span> b<span class="br0">)</span><span class="sy4">;</span></span></span>
</td></tr>
<tr>
<td> 乘法赋值
</td>
<td> <code>a *= b</code>
</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">是
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp">T<span class="sy3">&amp;</span> T<span class="sy4">::</span><span class="me2">operator</span> <span class="sy2">*</span><span class="sy1">=</span><span class="br0">(</span><span class="kw4">const</span> T2<span class="sy3">&amp;</span> b<span class="br0">)</span><span class="sy4">;</span></span></span>
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp">T<span class="sy3">&amp;</span> operator <span class="sy2">*</span><span class="sy1">=</span><span class="br0">(</span>T<span class="sy3">&amp;</span> a, <span class="kw4">const</span> T2<span class="sy3">&amp;</span> b<span class="br0">)</span><span class="sy4">;</span></span></span>
</td></tr>
<tr>
<td> 除法赋值
</td>
<td> <code>a /= b</code>
</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">是
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp">T<span class="sy3">&amp;</span> T<span class="sy4">::</span><span class="me2">operator</span> <span class="sy2">/</span><span class="sy1">=</span><span class="br0">(</span><span class="kw4">const</span> T2<span class="sy3">&amp;</span> b<span class="br0">)</span><span class="sy4">;</span></span></span>
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp">T<span class="sy3">&amp;</span> operator <span class="sy2">/</span><span class="sy1">=</span><span class="br0">(</span>T<span class="sy3">&amp;</span> a, <span class="kw4">const</span> T2<span class="sy3">&amp;</span> b<span class="br0">)</span><span class="sy4">;</span></span></span>
</td></tr>
<tr>
<td> 取模赋值
</td>
<td> <code>a %= b</code>
</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">是
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp">T<span class="sy3">&amp;</span> T<span class="sy4">::</span><span class="me2">operator</span> <span class="sy2">%</span><span class="sy1">=</span><span class="br0">(</span><span class="kw4">const</span> T2<span class="sy3">&amp;</span> b<span class="br0">)</span><span class="sy4">;</span></span></span>
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp">T<span class="sy3">&amp;</span> operator <span class="sy2">%</span><span class="sy1">=</span><span class="br0">(</span>T<span class="sy3">&amp;</span> a, <span class="kw4">const</span> T2<span class="sy3">&amp;</span> b<span class="br0">)</span><span class="sy4">;</span></span></span>
</td></tr>
<tr>
<td> 逐位与赋值
</td>
<td> <code>a &amp;= b</code>
</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">是
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp">T<span class="sy3">&amp;</span> T<span class="sy4">::</span><span class="me2">operator</span> <span class="sy3">&amp;</span><span class="sy1">=</span><span class="br0">(</span><span class="kw4">const</span> T2<span class="sy3">&amp;</span> b<span class="br0">)</span><span class="sy4">;</span></span></span>
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp">T<span class="sy3">&amp;</span> operator <span class="sy3">&amp;</span><span class="sy1">=</span><span class="br0">(</span>T<span class="sy3">&amp;</span> a, <span class="kw4">const</span> T2<span class="sy3">&amp;</span> b<span class="br0">)</span><span class="sy4">;</span></span></span>
</td></tr>
<tr>
<td> 逐位或赋值
</td>
<td> <code>a |= b</code>
</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">是
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp">T<span class="sy3">&amp;</span> T<span class="sy4">::</span><span class="me2">operator</span> <span class="sy3">|</span><span class="sy1">=</span><span class="br0">(</span><span class="kw4">const</span> T2<span class="sy3">&amp;</span> b<span class="br0">)</span><span class="sy4">;</span></span></span>
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp">T<span class="sy3">&amp;</span> operator <span class="sy3">|</span><span class="sy1">=</span><span class="br0">(</span>T<span class="sy3">&amp;</span> a, <span class="kw4">const</span> T2<span class="sy3">&amp;</span> b<span class="br0">)</span><span class="sy4">;</span></span></span>
</td></tr>
<tr>
<td> 逐位异或赋值
</td>
<td> <code>a ^= b</code>
</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">是
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp">T<span class="sy3">&amp;</span> T<span class="sy4">::</span><span class="me2">operator</span> <span class="sy3">^</span><span class="sy1">=</span><span class="br0">(</span><span class="kw4">const</span> T2<span class="sy3">&amp;</span> b<span class="br0">)</span><span class="sy4">;</span></span></span>
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp">T<span class="sy3">&amp;</span> operator <span class="sy3">^</span><span class="sy1">=</span><span class="br0">(</span>T<span class="sy3">&amp;</span> a, <span class="kw4">const</span> T2<span class="sy3">&amp;</span> b<span class="br0">)</span><span class="sy4">;</span></span></span>
</td></tr>
<tr>
<td> 逐位左移赋值
</td>
<td> <code>a &lt;&lt;= b</code>
</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">是
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp">T<span class="sy3">&amp;</span> T<span class="sy4">::</span><span class="me2">operator</span> <span class="sy1">&lt;&lt;=</span><span class="br0">(</span><span class="kw4">const</span> T2<span class="sy3">&amp;</span> b<span class="br0">)</span><span class="sy4">;</span></span></span>
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp">T<span class="sy3">&amp;</span> operator <span class="sy1">&lt;&lt;=</span><span class="br0">(</span>T<span class="sy3">&amp;</span> a, <span class="kw4">const</span> T2<span class="sy3">&amp;</span> b<span class="br0">)</span><span class="sy4">;</span></span></span>
</td></tr>
<tr>
<td> 逐位右移赋值
</td>
<td> <code>a &gt;&gt;= b</code>
</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">是
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp">T<span class="sy3">&amp;</span> T<span class="sy4">::</span><span class="me2">operator</span> <span class="sy1">&gt;&gt;=</span><span class="br0">(</span><span class="kw4">const</span> T2<span class="sy3">&amp;</span> b<span class="br0">)</span><span class="sy4">;</span></span></span>
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp">T<span class="sy3">&amp;</span> operator <span class="sy1">&gt;&gt;=</span><span class="br0">(</span>T<span class="sy3">&amp;</span> a, <span class="kw4">const</span> T2<span class="sy3">&amp;</span> b<span class="br0">)</span><span class="sy4">;</span></span></span>
</td></tr>
<tr>
<td colspan="5">
<dl><dd><b>注意</b><br>
</dd></dl>
<ul><li> 所有内建赋值运算符都返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span>，而大多数<a href="operators.html" title="cpp/language/operators">用户定义重载</a>亦返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span>，从而能以与内建版本相同的方式使用用户定义运算符。然而，用户定义运算符重载中，能以任何类型为返回类型（包括 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span></span></span>）。
</li><li> <code>T2</code> 可为包含 <code>T</code> 在内的任何类型
</li></ul>
</td></tr></table>
<h3><span class="mw-headline" id=".E8.A7.A3.E9.87.8A">解释</span></h3>
<p><i>复制赋值运算符</i>以 <code>b</code> 内容的副本替换对象 <code>a</code> 的内容（不修改 <code>b</code>）。对于类类型，这是一种特殊成员函数，描述于<a href="copy_assignment.html" title="cpp/language/copy assignment">复制赋值运算符</a>。
</p>
 <table class="t-rev-begin">
<tr class="t-rev t-since-cxx11"><td>
<p><i>移动赋值运算符</i>以 <code>b</code> 的内容替换对象 <code>a</code> 的内容，并尽可能避免复制（可以修改 <code>b</code>）。对于类类型，这是一种特殊成员函数，描述于<a href="move_assignment.html" title="cpp/language/move assignment">移动赋值运算符</a>。 <span class="t-mark-rev t-since-cxx11">(C++11 起)</span> 
</p>
</td>
<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td></tr>
</table>
<p>对于非类类型，对复制与移动赋值不加以区分，均被称作<i>直接赋值（direct assignment）</i>。
</p><p><i>复合赋值（compound assignment）</i>运算符以 <code>a</code> 的值和 <code>b</code> 的值间的二元运算结果替换对象 <code>a</code> 的内容。
</p>
<h4><span class="mw-headline" id=".E5.86.85.E5.BB.BA.E7.9A.84.E7.9B.B4.E6.8E.A5.E8.B5.8B.E5.80.BC">内建的直接赋值</span></h4>
<p>直接赋值表达式的形式为
</p>
<table class="t-sdsc-begin">

<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <span class="t-spar">lhs</span> <code><b>=</b></code> <span class="t-spar">rhs</span>
</td>
<td> (1)
</td>
<td class="t-sdsc-nopad">
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <span class="t-spar">lhs</span> <code><b>=</b></code> <code><b>{} </b></code>
</td>
<td> (2)
</td>
<td> <span class="t-mark-rev t-since-cxx11">(C++11 起)</span>
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <span class="t-spar">lhs</span> <code><b>=</b></code> <code><b>{ </b></code> <span class="t-spar">rhs</span> <code><b>} </b></code>
</td>
<td> (3)
</td>
<td> <span class="t-mark-rev t-since-cxx11">(C++11 起)</span>
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr></table>
<p>对于内建运算符，<span class="t-spar">lhs</span> 可拥有任何非 const 标量类型，而 <span class="t-spar">rhs</span> 必须可隐式转换为 <span class="t-spar">lhs</span> 的类型。
</p><p>直接赋值运算符期待以一个可修改左值为其左操作数，以一个右值表达式<span class="t-rev-inl t-since-cxx11"><span>或<i>花括号初始化器列表</i></span> <span><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></span></span>为其右操作数，并返回一个标识修改后的左运操作的左值。
</p><p>对于非类类型，首先将右操作数<a href="implicit_cast.html" title="cpp/language/implicit conversion">隐式转换</a>为左操作数的无 cv 限定的类型，然后复制其值到左操作数所标识的对象中。
</p><p>当左操作数拥有引用类型时，赋值运算符修改被引用的对象。
</p><p>若左右操作数标识的对象之间有重叠，则行为未定义（除非二者严格重叠且类型相同）。
</p>
 <table class="t-rev-begin">
<tr class="t-rev t-since-cxx11"><td>
<p>当右运算数为<i>花括号初始化器列表 (brace-init-list)</i>时
</p>
<ul><li> 若表达式 <code>E1</code> 拥有标量类型，则
</li></ul>
<dl><dd><ul><li> 表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp">E1 <span class="sy1">=</span> <span class="br0">{</span><span class="br0">}</span></span></span> 等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp">E1 <span class="sy1">=</span> T<span class="br0">{</span><span class="br0">}</span></span></span>，其中 <code>T</code> 是 <code>E1</code> 的类型。
</li><li> 表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp">E1 <span class="sy1">=</span> <span class="br0">{</span>E2<span class="br0">}</span></span></span> 等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp">E1 <span class="sy1">=</span> T<span class="br0">{</span>E2<span class="br0">}</span></span></span>，其中 <code>T</code> 是 <code>E1</code> 的类型。
</li></ul>
</dd></dl>
<ul><li> 若表达式 <code>E1</code> 拥有类类型，则语法 <span class="t-c"><span class="mw-geshi cpp source-cpp">E1 <span class="sy1">=</span> <span class="br0">{</span>args...<span class="br0">}</span></span></span> 生成以<i>花括号初始化器列表</i>为实参对赋值运算符的一次调用，然后遵循<a href="overload_resolution.html" title="cpp/language/overload resolution">重载决议</a>规则选取适合的赋值运算符。需要注意的是，若以某个非类类型为实参的非模板赋值运算符可用，则它胜过 <code>E1 = {} </code> 中的复制/移动赋值，这是因为从 <code>{} </code> 到非类类型属于<a href="overload_resolution.html#.E5.88.97.E8.A1.A8.E5.88.9D.E5.A7.8B.E5.8C.96.E4.B8.AD.E7.9A.84.E9.9A.90.E5.BC.8F.E8.BD.AC.E6.8D.A2.E5.BA.8F.E5.88.97" title="cpp/language/overload resolution">恒等转换</a>，它优先于从 <code>{} </code> 到类类型的用户定义转换。
</li></ul>
</td>
<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td></tr>
</table>
 <table class="t-rev-begin">
<tr class="t-rev t-since-cxx20"><td>
<p>以 volatile 限定的非类类型左值为内建直接赋值运算符的左操作数被弃用，除非该赋值表达式出现于<a href="expressions.html#.E4.B8.8D.E6.B1.82.E5.80.BC.E8.A1.A8.E8.BE.BE.E5.BC.8F" title="cpp/language/expressions">不求值语境</a>或是<a href="expressions.html#.E5.BC.83.E5.80.BC.E8.A1.A8.E8.BE.BE.E5.BC.8F" title="cpp/language/expressions">弃值表达式</a>。
</p>
</td>
<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td></tr>
</table>
<p><a href="overload_resolution.html#.E8.B0.83.E7.94.A8.E9.87.8D.E8.BD.BD.E8.BF.90.E7.AE.97.E7.AC.A6" title="cpp/language/overload resolution">针对用户定义运算符的重载决议</a>中，对于每个类型 <code>T</code>，下列函数签名参与重载决议：
</p>
<table class="t-dcl-begin"><tbody>
<tr class="t-dcl">
<td class="t-dcl-nopad"> <div><span class="mw-geshi cpp source-cpp">T<span class="sy2">*</span><span class="sy3">&amp;</span> operator<span class="sy1">=</span><span class="br0">(</span>T<span class="sy2">*</span><span class="sy3">&amp;</span>, T<span class="sy2">*</span><span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td class="t-dcl-nopad">  </td>
<td class="t-dcl-nopad">  </td>
</tr>
<tr class="t-dcl">
<td class="t-dcl-nopad"> <div><span class="mw-geshi cpp source-cpp">T<span class="sy2">*</span><span class="kw4">volatile</span> <span class="sy3">&amp;</span> operator<span class="sy1">=</span><span class="br0">(</span>T<span class="sy2">*</span><span class="kw4">volatile</span> <span class="sy3">&amp;</span>, T<span class="sy2">*</span><span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td class="t-dcl-nopad">  </td>
<td class="t-dcl-nopad">  </td>
</tr>
<tr class="t-dcl-sep"><td></td><td></td><td></td></tr>
</tbody></table>
<p>对于每个枚举或成员指针类型 <code>T</code>（可选地有 volatile 限定），下列函数签名参与重载决议：
</p>
<table class="t-dcl-begin"><tbody>
<tr class="t-dcl">
<td class="t-dcl-nopad"> <div><span class="mw-geshi cpp source-cpp">T<span class="sy3">&amp;</span> operator<span class="sy1">=</span><span class="br0">(</span>T<span class="sy3">&amp;</span>, T <span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td class="t-dcl-nopad">  </td>
<td class="t-dcl-nopad">  </td>
</tr>
<tr class="t-dcl-sep"><td></td><td></td><td></td></tr>
</tbody></table>
<p>对于每对 A1 和 A2，其中 A1 是算术类型（可选地有 volatile 限定）而 A2 是提升后的算术类型，下列函数签名参与重载决议：
</p>
<table class="t-dcl-begin"><tbody>
<tr class="t-dcl">
<td class="t-dcl-nopad"> <div><span class="mw-geshi cpp source-cpp">A1<span class="sy3">&amp;</span> operator<span class="sy1">=</span><span class="br0">(</span>A1<span class="sy3">&amp;</span>, A2<span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td class="t-dcl-nopad">  </td>
<td class="t-dcl-nopad">  </td>
</tr>
<tr class="t-dcl-sep"><td></td><td></td><td></td></tr>
</tbody></table>
<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
<div class="t-example"><div class="t-example-live-link"><div class="coliru-btn coliru-btn-run-init">运行此代码</div></div>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="co2">#include &lt;iostream&gt;</span>
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
<span class="br0">{</span>
    <span class="kw4">int</span> n <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span>  <span class="co1">// 不是赋值</span>
    n <span class="sy1">=</span> <span class="nu0">1</span><span class="sy4">;</span>      <span class="co1">// 直接赋值</span>
    <a href="../io/cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> n <span class="sy1">&lt;&lt;</span> <span class="st0">' '</span><span class="sy4">;</span>
    n <span class="sy1">=</span> <span class="br0">{</span><span class="br0">}</span><span class="sy4">;</span>     <span class="co1">// 零初始化，然后赋值</span>
    <a href="../io/cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> n <span class="sy1">&lt;&lt;</span> <span class="st0">' '</span><span class="sy4">;</span>
    n <span class="sy1">=</span> <span class="st0">'a'</span><span class="sy4">;</span>    <span class="co1">// 整型提升，然后赋值</span>
    <a href="../io/cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> n <span class="sy1">&lt;&lt;</span> <span class="st0">' '</span><span class="sy4">;</span>
    n <span class="sy1">=</span> <span class="br0">{</span><span class="st0">'b'</span><span class="br0">}</span><span class="sy4">;</span>   <span class="co1">// 显式转型，然后赋值</span>
    <a href="../io/cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> n <span class="sy1">&lt;&lt;</span> <span class="st0">' '</span><span class="sy4">;</span>
    n <span class="sy1">=</span> <span class="nu16">1.0</span><span class="sy4">;</span>    <span class="co1">// 浮点转换，然后赋值</span>
    <a href="../io/cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> n <span class="sy1">&lt;&lt;</span> <span class="st0">' '</span><span class="sy4">;</span>
<span class="co1">//    n = {1.0}; // 编译错误（窄化转换）</span>
 
    <span class="kw4">int</span><span class="sy3">&amp;</span> r <span class="sy1">=</span> n<span class="sy4">;</span>  <span class="co1">// 不是赋值</span>
    <span class="kw4">int</span><span class="sy2">*</span> p<span class="sy4">;</span>
 
    r <span class="sy1">=</span> <span class="nu0">2</span><span class="sy4">;</span>       <span class="co1">// 通过引用赋值</span>
    <a href="../io/cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> n <span class="sy1">&lt;&lt;</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
    p <span class="sy1">=</span> <span class="sy3">&amp;</span>n<span class="sy4">;</span>      <span class="co1">// 直接赋值</span>
    p <span class="sy1">=</span> nullptr<span class="sy4">;</span> <span class="co1">// 空指针转换，然后赋值</span>
 
    <span class="kw1">struct</span> <span class="br0">{</span><span class="kw4">int</span> a<span class="sy4">;</span> <a href="../string/basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> s<span class="sy4">;</span><span class="br0">}</span> obj<span class="sy4">;</span>
    obj <span class="sy1">=</span> <span class="br0">{</span><span class="nu0">1</span>, <span class="st0">"abc"</span><span class="br0">}</span><span class="sy4">;</span> <span class="co1">// 从花括号初始化器列表赋值</span>
    <a href="../io/cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> obj.<span class="me1">a</span> <span class="sy1">&lt;&lt;</span> <span class="st0">':'</span> <span class="sy1">&lt;&lt;</span> obj.<span class="me1">s</span> <span class="sy1">&lt;&lt;</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
<span class="br0">}</span></pre></div></div>
<p>输出：
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="text source-text"><pre class="de1">1 0 97 98 1 2
1:abc</pre></div></div> 
</div>
<h4><span class="mw-headline" id=".E5.86.85.E5.BB.BA.E7.9A.84.E5.A4.8D.E5.90.88.E8.B5.8B.E5.80.BC">内建的复合赋值</span></h4>
<p>复合赋值表达式的形式为
</p>
<table class="t-sdsc-begin">

<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <span class="t-spar">lhs</span> <span class="t-spar">op</span> <span class="t-spar">rhs</span>
</td>
<td> (1)
</td>
<td class="t-sdsc-nopad">
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> lhs <span class="t-spar">op</span> {}
</td>
<td> (2)
</td>
<td> <span class="t-mark-rev t-since-cxx11">(C++11 起)</span>
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> lhs <span class="t-spar">op</span> {rhs}
</td>
<td> (3)
</td>
<td> <span class="t-mark-rev t-since-cxx11">(C++11 起)</span>
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr></table>
<table class="t-par-begin">


<tr class="t-par">
<td>  <span class="t-spar">op</span>
</td>
<td> -
</td>
<td>  <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span><span class="sy1">=</span></span></span>、<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">/</span><span class="sy1">=</span></span></span>、<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">%</span><span class="sy1">=</span></span></span>、<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">+</span><span class="sy1">=</span></span></span>、<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">-</span><span class="sy1">=</span></span></span>、<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy1">&lt;&lt;=</span></span></span>、<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy1">&gt;&gt;=</span></span></span>、<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy3">&amp;</span><span class="sy1">=</span></span></span>、<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy3">^</span><span class="sy1">=</span></span></span>、<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy3">|</span><span class="sy1">=</span></span></span> 之一
</td></tr>
<tr class="t-par">
<td>  <span class="t-spar">lhs</span>
</td>
<td> -
</td>
<td> 对于内建运算符，<span class="t-spar">lhs</span> 可具有任何算术类型，但若 <span class="t-spar">op</span> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">+</span><span class="sy1">=</span></span></span> 或 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">-</span><span class="sy1">=</span></span></span>，则也接受指针类型，并与 + 和 - 有相同限制
</td></tr>
<tr class="t-par">
<td>  <span class="t-spar">rhs</span>
</td>
<td> -
</td>
<td> 对于内建运算符，<span class="t-spar">rhs</span> 必须可隐式转换为 <span class="t-spar">lhs</span>
</td></tr></table>
<p>每个内建复合赋值运算符表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp">E1 op<span class="sy1">=</span> E2</span></span>（其中 E1 是可修改左值表达式，而 E2 是右值表达式<span class="t-rev-inl t-since-cxx11"><span>或<i>花括号初始化器列表</i></span> <span><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></span></span>）的行为与表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp">E1 <span class="sy1">=</span> E1 op E2</span></span> 的行为严格相同，但只对表达式 <code>E1</code> 进行一次求值，并且对于顺序不确定的函数而言是一次单个操作（例如 <span class="t-c"><span class="mw-geshi cpp source-cpp">f<span class="br0">(</span>a <span class="sy2">+</span><span class="sy1">=</span> b, g<span class="br0">(</span><span class="br0">)</span><span class="br0">)</span></span></span> 中，从 <span class="t-c"><span class="mw-geshi cpp source-cpp">g<span class="br0">(</span><span class="br0">)</span></span></span> 内来看，+= 要么完全未开始，要么已完成）。
</p>
 <table class="t-rev-begin">
<tr class="t-rev t-since-cxx20"><td>
<p>以 volatile 限定的非类类型左值为内建复合赋值运算符的左操作数被弃用。
</p>
</td>
<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td></tr>
</table>
<p>在<a href="overload_resolution.html#.E8.B0.83.E7.94.A8.E9.87.8D.E8.BD.BD.E8.BF.90.E7.AE.97.E7.AC.A6" title="cpp/language/overload resolution">针对用户定义运算符的重载决议</a>中，对每对 A1 和 A2，其中 A1 是算术类型（可选地有 volatile 限定）而 A2 为提升后的算术类型，下列函数签名参与重载决议：
</p>
<table class="t-dcl-begin"><tbody>
<tr class="t-dcl">
<td class="t-dcl-nopad"> <div><span class="mw-geshi cpp source-cpp">A1<span class="sy3">&amp;</span> operator<span class="sy2">*</span><span class="sy1">=</span><span class="br0">(</span>A1<span class="sy3">&amp;</span>, A2<span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td class="t-dcl-nopad">  </td>
<td class="t-dcl-nopad">  </td>
</tr>
<tr class="t-dcl">
<td class="t-dcl-nopad"> <div><span class="mw-geshi cpp source-cpp">A1<span class="sy3">&amp;</span> operator<span class="sy2">/</span><span class="sy1">=</span><span class="br0">(</span>A1<span class="sy3">&amp;</span>, A2<span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td class="t-dcl-nopad">  </td>
<td class="t-dcl-nopad">  </td>
</tr>
<tr class="t-dcl">
<td class="t-dcl-nopad"> <div><span class="mw-geshi cpp source-cpp">A1<span class="sy3">&amp;</span> operator<span class="sy2">+</span><span class="sy1">=</span><span class="br0">(</span>A1<span class="sy3">&amp;</span>, A2<span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td class="t-dcl-nopad">  </td>
<td class="t-dcl-nopad">  </td>
</tr>
<tr class="t-dcl">
<td class="t-dcl-nopad"> <div><span class="mw-geshi cpp source-cpp">A1<span class="sy3">&amp;</span> operator<span class="sy2">-</span><span class="sy1">=</span><span class="br0">(</span>A1<span class="sy3">&amp;</span>, A2<span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td class="t-dcl-nopad">  </td>
<td class="t-dcl-nopad">  </td>
</tr>
<tr class="t-dcl-sep"><td></td><td></td><td></td></tr>
</tbody></table>
<p>对于每对 I1 与 I2，其中 I1 是整型类型（可选地有 volatile 限定）而 I2 为提升后的整型类型，下列函数签名参与重载决议：
</p>
<table class="t-dcl-begin"><tbody>
<tr class="t-dcl">
<td class="t-dcl-nopad"> <div><span class="mw-geshi cpp source-cpp">I1<span class="sy3">&amp;</span> operator<span class="sy2">%</span><span class="sy1">=</span><span class="br0">(</span>I1<span class="sy3">&amp;</span>, I2<span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td class="t-dcl-nopad">  </td>
<td class="t-dcl-nopad">  </td>
</tr>
<tr class="t-dcl">
<td class="t-dcl-nopad"> <div><span class="mw-geshi cpp source-cpp">I1<span class="sy3">&amp;</span> operator<span class="sy1">&lt;&lt;=</span><span class="br0">(</span>I1<span class="sy3">&amp;</span>, I2<span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td class="t-dcl-nopad">  </td>
<td class="t-dcl-nopad">  </td>
</tr>
<tr class="t-dcl">
<td class="t-dcl-nopad"> <div><span class="mw-geshi cpp source-cpp">I1<span class="sy3">&amp;</span> operator<span class="sy1">&gt;&gt;=</span><span class="br0">(</span>I1<span class="sy3">&amp;</span>, I2<span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td class="t-dcl-nopad">  </td>
<td class="t-dcl-nopad">  </td>
</tr>
<tr class="t-dcl">
<td class="t-dcl-nopad"> <div><span class="mw-geshi cpp source-cpp">I1<span class="sy3">&amp;</span> operator<span class="sy3">&amp;</span><span class="sy1">=</span><span class="br0">(</span>I1<span class="sy3">&amp;</span>, I2<span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td class="t-dcl-nopad">  </td>
<td class="t-dcl-nopad">  </td>
</tr>
<tr class="t-dcl">
<td class="t-dcl-nopad"> <div><span class="mw-geshi cpp source-cpp">I1<span class="sy3">&amp;</span> operator<span class="sy3">^</span><span class="sy1">=</span><span class="br0">(</span>I1<span class="sy3">&amp;</span>, I2<span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td class="t-dcl-nopad">  </td>
<td class="t-dcl-nopad">  </td>
</tr>
<tr class="t-dcl">
<td class="t-dcl-nopad"> <div><span class="mw-geshi cpp source-cpp">I1<span class="sy3">&amp;</span> operator<span class="sy3">|</span><span class="sy1">=</span><span class="br0">(</span>I1<span class="sy3">&amp;</span>, I2<span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td class="t-dcl-nopad">  </td>
<td class="t-dcl-nopad">  </td>
</tr>
<tr class="t-dcl-sep"><td></td><td></td><td></td></tr>
</tbody></table>
<p>对于每个可选地有 cv 限定的对象类型 <code>T</code>，下列函数签名参与重载决议：
</p>
<table class="t-dcl-begin"><tbody>
<tr class="t-dcl">
<td class="t-dcl-nopad"> <div><span class="mw-geshi cpp source-cpp">T<span class="sy2">*</span><span class="sy3">&amp;</span> operator<span class="sy2">+</span><span class="sy1">=</span><span class="br0">(</span>T<span class="sy2">*</span><span class="sy3">&amp;</span>, <a href="../types/ptrdiff_t.html"><span class="kw101">std::<span class="me2">ptrdiff_t</span></span></a><span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td class="t-dcl-nopad">  </td>
<td class="t-dcl-nopad">  </td>
</tr>
<tr class="t-dcl">
<td class="t-dcl-nopad"> <div><span class="mw-geshi cpp source-cpp">T<span class="sy2">*</span><span class="sy3">&amp;</span> operator<span class="sy2">-</span><span class="sy1">=</span><span class="br0">(</span>T<span class="sy2">*</span><span class="sy3">&amp;</span>, <a href="../types/ptrdiff_t.html"><span class="kw101">std::<span class="me2">ptrdiff_t</span></span></a><span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td class="t-dcl-nopad">  </td>
<td class="t-dcl-nopad">  </td>
</tr>
<tr class="t-dcl">
<td class="t-dcl-nopad"> <div><span class="mw-geshi cpp source-cpp">T<span class="sy2">*</span><span class="kw4">volatile</span> <span class="sy3">&amp;</span> operator<span class="sy2">+</span><span class="sy1">=</span><span class="br0">(</span>T<span class="sy2">*</span><span class="kw4">volatile</span> <span class="sy3">&amp;</span>, <a href="../types/ptrdiff_t.html"><span class="kw101">std::<span class="me2">ptrdiff_t</span></span></a><span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td class="t-dcl-nopad">  </td>
<td class="t-dcl-nopad">  </td>
</tr>
<tr class="t-dcl">
<td class="t-dcl-nopad"> <div><span class="mw-geshi cpp source-cpp">T<span class="sy2">*</span><span class="kw4">volatile</span> <span class="sy3">&amp;</span> operator<span class="sy2">-</span><span class="sy1">=</span><span class="br0">(</span>T<span class="sy2">*</span><span class="kw4">volatile</span> <span class="sy3">&amp;</span>, <a href="../types/ptrdiff_t.html"><span class="kw101">std::<span class="me2">ptrdiff_t</span></span></a><span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td class="t-dcl-nopad">  </td>
<td class="t-dcl-nopad">  </td>
</tr>
<tr class="t-dcl-sep"><td></td><td></td><td></td></tr>
</tbody></table>
<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B_2">示例</span></h3>
<table class="metadata plainlinks ambox mbox-small-left ambox-notice" style=""><tr><td class="mbox-empty-cell"></td><td class="mbox-text" style="">本节未完成<br>原因：暂无示例 </td></tr></table>
<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
<p><a href="operator_precedence.html" title="cpp/language/operator precedence">运算符优先级</a>
</p><p><a href="operators.html" title="cpp/language/operators">运算符重载</a>
</p>
<table class="wikitable">

<tr style="text-align:center">
<th colspan="7">常见运算符
</th></tr>
<tr style="text-align:center">
<td> <strong class="selflink">赋值</strong>
</td>
<td> <a href="operator_incdec.html" title="cpp/language/operator incdec">自增<br>自减</a>
</td>
<td> <a href="operator_arithmetic.html" title="cpp/language/operator arithmetic">算术</a>
</td>
<td> <a href="operator_logical.html" title="cpp/language/operator logical">逻辑</a>
</td>
<td> <a href="operator_comparison.html" title="cpp/language/operator comparison">比较</a>
</td>
<td> <a href="operator_member_access.html" title="cpp/language/operator member access">成员访问</a>
</td>
<td> <a href="operator_other.html" title="cpp/language/operator other">其他</a>
</td></tr>
<tr style="text-align:center">
<td>
<p><span class="t-c"><span class="mw-geshi cpp source-cpp">a <span class="sy1">=</span> b<br>
a <span class="sy2">+</span><span class="sy1">=</span> b<br>
a <span class="sy2">-</span><span class="sy1">=</span> b<br>
a <span class="sy2">*</span><span class="sy1">=</span> b<br>
a <span class="sy2">/</span><span class="sy1">=</span> b<br>
a <span class="sy2">%</span><span class="sy1">=</span> b<br>
a <span class="sy3">&amp;</span><span class="sy1">=</span> b<br>
a <span class="sy3">|</span><span class="sy1">=</span> b<br>
a <span class="sy3">^</span><span class="sy1">=</span> b<br>
a <span class="sy1">&lt;&lt;=</span> b<br>
a <span class="sy1">&gt;&gt;=</span> b</span></span>
</p>
</td>
<td>
<p><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">++</span>a<br>
<span class="sy2">--</span>a<br>
a<span class="sy2">++</span><br>
a<span class="sy2">--</span></span></span>
</p>
</td>
<td>
<p><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">+</span>a<br>
<span class="sy2">-</span>a<br>
a <span class="sy2">+</span> b<br>
a <span class="sy2">-</span> b<br>
a <span class="sy2">*</span> b<br>
a <span class="sy2">/</span> b<br>
a <span class="sy2">%</span> b<br>
~a<br>
a <span class="sy3">&amp;</span> b<br>
a <span class="sy3">|</span> b<br>
a <span class="sy3">^</span> b<br>
a <span class="sy1">&lt;&lt;</span> b<br>
a <span class="sy1">&gt;&gt;</span> b</span></span>
</p>
</td>
<td>
<p><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy3">!</span>a<br>
a <span class="sy3">&amp;&amp;</span> b<br>
a <span class="sy3">||</span> b</span></span>
</p>
</td>
<td>
<p><span class="t-c"><span class="mw-geshi cpp source-cpp">a <span class="sy1">==</span> b<br>
a <span class="sy3">!</span><span class="sy1">=</span> b<br>
a <span class="sy1">&lt;</span> b<br>
a <span class="sy1">&gt;</span> b<br>
a <span class="sy1">&lt;=</span> b<br>
a <span class="sy1">&gt;=</span> b<br>
a <span class="sy1">&lt;=&gt;</span> b</span></span>
</p>
</td>
<td>
<p><span class="t-c"><span class="mw-geshi cpp source-cpp">a<span class="br0">[</span>b<span class="br0">]</span><br>
<span class="sy2">*</span>a<br>
<span class="sy3">&amp;</span>a<br>
a<span class="sy2">-</span><span class="sy1">&gt;</span>b<br>
a.<span class="me1">b</span><br>
a<span class="sy2">-</span><span class="sy1">&gt;</span><span class="sy2">*</span>b<br>
a.<span class="sy2">*</span>b</span></span>
</p>
</td>
<td>
<p><span class="t-c"><span class="mw-geshi cpp source-cpp">a<span class="br0">(</span>...<span class="br0">)</span><br>
a, b<br>
<span class="sy4">?</span> <span class="sy4">:</span></span></span>
</p>
</td></tr>
<tr>
<th colspan="7">特殊运算符
</th></tr>
<tr>
<td colspan="7">
<p><a href="static_cast.html" title="cpp/language/static cast"><tt>static_cast</tt></a> 转换一个类型为另一相关类型<br>
<a href="dynamic_cast.html" title="cpp/language/dynamic cast"><tt>dynamic_cast</tt></a> 在继承层级中转换<br>
<a href="const_cast.html" title="cpp/language/const cast"><tt>const_cast</tt></a> 添加或移除 <a href="cv.html" title="cpp/language/cv">cv</a> 限定符<br>
<a href="reinterpret_cast.html" title="cpp/language/reinterpret cast"><tt>reinterpret_cast</tt></a> 转换类型到无关类型<br>
<a href="explicit_cast.html" title="cpp/language/explicit cast">C 风格转型</a> 以 <code>static_cast</code> 、 <code>const_cast</code> 及 <code>reinterpret_cast</code> 的混合转换一个类型到另一类型<br>
<a href="new.html" title="cpp/language/new"><tt>new</tt></a> 创建有动态存储期的对象<br>
<a href="delete.html" title="cpp/language/delete"><tt>delete</tt></a> 销毁先前由 new 表达式创建的对象，并释放其所拥有的内存区域<br>
<a href="sizeof.html" title="cpp/language/sizeof"><tt>sizeof</tt></a> 查询类型的大小<br>
<a href="sizeof....html" title="cpp/language/sizeof..."><tt>sizeof...</tt></a> 查询<a href="parameter_pack.html" title="cpp/language/parameter pack">形参包</a>的大小<span class="t-mark-rev t-since-cxx11">(C++11 起)</span><br>
<a href="typeid.html" title="cpp/language/typeid"><tt>typeid</tt></a> 查询类型的类型信息<br>
<a href="noexcept.html" title="cpp/language/noexcept"><tt>noexcept</tt></a> 查询表达式是否能抛出异常<span class="t-mark-rev t-since-cxx11">(C++11 起)</span><br>
<a href="alignof.html" title="cpp/language/alignof"><tt>alignof</tt></a> 查询类型的对齐要求<span class="t-mark-rev t-since-cxx11">(C++11 起)</span>
</p>
</td></tr></table>
<table class="t-dsc-begin">

</table>

<!-- 
NewPP limit report
Preprocessor visited node count: 6339/1000000
Preprocessor generated node count: 13265/1000000
Post‐expand include size: 90553/2097152 bytes
Template argument size: 21295/2097152 bytes
Highest expansion depth: 19/40
Expensive parser function count: 0/100
-->

<!-- Saved in parser cache with key mwiki1-mwiki_zh_:pcache:idhash:2736-0!*!0!!zh!*!zh!* and timestamp 20200210062350 -->
</div>                    <!-- /bodycontent -->
                                        <!-- printfooter -->
                    <div class="printfooter">
                    来自“<a href="https://zh.cppreference.com/mwiki/index.php?title=cpp/language/operator_assignment&amp;oldid=64608">https://zh.cppreference.com/mwiki/index.php?title=cpp/language/operator_assignment&amp;oldid=64608</a>”                    </div>
                    <!-- /printfooter -->
                                                            <!-- catlinks -->
                    <!-- /catlinks -->
                                                            <div class="visualClear"></div>
                    <!-- debughtml -->
                                        <!-- /debughtml -->
                </div>
                <!-- /bodyContent -->
            </div>
        </div>
        <!-- /content -->
        <!-- footer -->
        <div id="cpp-footer-base" class="noprint">
            <div id="footer">
                        <div id="cpp-navigation">
            <h5>导航</h5>
            <ul><li><a href="https://zh.cppreference.com/w/cpp/language/operator_assignment">Online version</a></li><li>Offline version retrieved 2020-03-14 18:00.</li></ul></div>
                        <ul id="footer-info">
                                    <li id="footer-info-lastmod"> 本页面最后修改于2020年2月9日 (星期日) 22:23。</li>
                                    <li id="footer-info-viewcount">此页面已被浏览过6,440次。</li>
                            </ul>
                    </div>
        </div>
        <!-- /footer -->
        <script>if(window.mw){
mw.loader.state({"site":"loading","user":"missing","user.groups":"ready"});
}</script>
<script src="../../../common/skin_scripts.js"></script>
<script>if(window.mw){
mw.loader.load(["mediawiki.action.view.postEdit","mediawiki.user","mediawiki.page.ready","mediawiki.searchSuggest","mediawiki.hidpi","ext.gadget.MathJax","ext.gadget.ColiruCompiler"], null, true);
}</script>
<script src="../../../common/site_scripts.js"></script>
<script type="text/javascript">
var _gaq = _gaq || [];
_gaq.push(['_setAccount', 'UA-2828341-1']);
_gaq.push(['_setDomainName', 'cppreference.com']);
_gaq.push(['_trackPageview']);
</script><!-- Served in 0.074 secs. -->
	</body>
<!-- Cached 20200211032441 -->
</html>